Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2001-08-27
2003-05-27
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S900000, C208S020000, C208S021000
Reexamination Certificate
active
06569235
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to apparatus and methods for in situ construction of subsurface containment barriers for containing hazardous waste materials buried under the earth, and more particularly to a method of constructing a vault to encapsulate such hazardous materials so that contaminants are not released into the air or surrounding or underlying strata. The present invention further relates to a means for monitoring the continued integrity of the vault over many years and to a means for repairing any breaches which might occur over time.
BACKGROUND OF THE INVENTION
In the early days of the nuclear age, contaminated debris and undocumented low level radioactive waste were buried in shallow trenches. Other waste materials were placed in underground storage tanks. These burial areas are now considered to pose a unacceptable risk to the environment. Excavation and removal of these wastes is potentially dangerous and very expensive. The concern is that excavation of such sites could release airborne radioactive contaminants which would pose a substantial harm to personnel and nearby residents. There have been a number of solutions proposed for containing these sites. Some of these solutions include slant drilled jet grouting, soil freezing, soil dehydration, tunneling, and chemical grout permeation. Others have taught vertical drilling and hydraulic fracturing as a means of forming a bottom barrier.
U.S. Pat. No. 4,230,368 and 4,491,369 to Cleary and others have disclosed the concept of displacing soil blocks containing the contaminants. This is accomplished by making a narrow vertical trench around the perimeter of the soil and forming a horizontal fracture under the site, through injection of a fluid under pressure. The horizontal fracture intersects the vertical perimeter trench. A seal is created along the surface areas of the vertical perimeter trench as continued injection of pressurized fluid into the horizontal fracture causes the block of soil within the perimeter to be lifted upwards.
The injected fluid may also become a sealant to produce a barrier surrounding the block like a basement. U.S. Pat. No. 4,230,368 to Cleary discloses that the density of the fluid is a factor in reducing the pressure needed to displace the block but does not contemplate use of fluid densities greater than those achievable with locally excavated soil materials in a clay slurry. This is by definition, less dense than soil. Gel strength of the fluid is mentioned as the primary means of sealing the perimeter opening. Such methods produce both the initial fracture and upward displacement by increasing hydrostatic pressure on the bottom of the block.
The problem with this approach is that hydrostatic pressure will cause fractures to propagate along the plane of least principal stresses. It is not possible to verify the final location and limits of such fractures in a radioactive waste site. The thickness and continuity of such fractures can not be verified. Because of the potential for uncontrolled fracturing into and beyond the contaminated material this method has not been used to produce any type of containment structure in radioactive waste sites.
The inventor's previous invention, U.S. Pat. No. 5,542,782, which is hereby incorporated by reference, describes a means of cutting vertical and horizontal barriers with high pressure jets of grout slurry and teaches the benefits of constructing such barriers from grout materials which are of a density equal to or greater than that of the overburden. This reference also teaches that the thickness of a horizontal grout barrier may be increased by introduction of a grout slurry which is sufficiently dense so as to result in net upward forces on the soil which heave the land surface upward, however few details of the method or apparatus to accomplish this are described.
SUMMARY OF THE INVENTION
The present invention is directed to improved methods and apparatus for constructing a thick horizontal barrier through buoyant block displacement. The present invention provides a new means for cutting the soil with a cable saw and details a practical apparatus for introducing a block displacement fluid to multiple cuts under a large multi-acre site. The subject invention also provides an improved means of cutting a thin horizontal barrier with high pressure jetting apparatus, which is more practical for application of chemical grouts and has an improved means of joining adjacent cuts to previous ones and recovering from equipment breakage.
The present invention uses a combination of trenching, horizontal directional drilling, diamond wire quarry saw methods, or high pressure jetting to cut a thin gap under and around a block of soil containing the contamination. As this “cut” is formed, it is filled with a high-density low-viscosity fluid grout. This thin channel of this dense fluid extends back to the surface and so exerts a hydrostatic head against the soil. This proprietary fluid is so heavy that the soil and rock will literally float on a thin layer of the fluid. This keeps the cut open and prevents the weight of the soil block from squeezing the fluid out from under it. After the block has been completely cut loose from the earth, additional dense fluid is pumped and poured into the cut. This additional fluid exerts a buoyant force on the block and causes it to rise out of the earth. The dense fluid is designed to slowly harden over a period of weeks to form an impermeable barrier. Use of the head of the dense grout fluid instead of attempting to pressurize the fluid to support the block is a subtle but important innovation. It eliminates the difficulties of sealing the vertical perimeter trench and also prevents uncontrolled fracturing of the grout into the waste burial area. If any of the grout fluid should find a crack in the active waste area it will do no more than fill it. It can not spurt up to the surface and form fountains of contaminated liquid, as it could do if it were under pressure. While the grout under the block is liquid an impermeable barrier sheet, such as HDPE (high density polyethylene extrusion), may be pulled under the floating block.
After the “moat-like” barrier around the soil block has hardened, a gravity-anchored, airtight cap structure is built on top of it. The HDPE liner under the block may be fission bonded to the HDPE liner in the cap to achieve a very high degree of containment integrity. Passive soil gas pressure sensors under the cap and similar sensors in the ground outside the cap monitor the air pressure changes inside the structure as a function of normal atmospheric pressure changes due to weather. This data allows passive monitoring of the integrity of not only the horizontal barrier but also the entire containment structure. Moisture, sound, and chemical tracer levels may be passively monitored as leak and leak location indicators, Repair of damage is also possible by flooding the structure with liquid grout.
A wire saw may also be used with molten paraffin grout to form a thin barrier roughly the thickness of the steel cable. This method maintains a circulating supply of molten paraffin in the pulling pipes which is ejected through holes in the pipe adjacent to the area being cut. The steel cable carries this molten paraffin into the cut and back to the surface. The paraffin is modified with additives that cause it to permeate into tight soils and form a barrier significantly thicker than the cut. Rapid cooling of the grout as the cut proceeds prevent excessive subsidence. An unlimited number of replacement jetting tubes or wire saw cables may be pulled into cutting position by the steel cables or the heated “pulling pipes” which are in the original directionally drilled holes. These may remelt a path through the previous cut.
Improvements on the inventor's previously disclosed method of forming a barrier by high pressure jetting from a long arcuate conduit are also described. The new method forms a very thin cut using chemical grout, such as molten paraffin or
Howrey Simon Arnold & White , LLP
Marcantoni Paul
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